Rubella infection in the United States now is distinctly uncommon. Between 1990 and 1999, the median annual number of reported rubella cases was 232. In only one of the years between 1992 and 1999 were more than 300 cases reported. During this time, the incidence of rubella infection in children younger than 15 years decreased from 0.63 to 0.06 in 100,000 whereas the incidence in adults increased slightly from 0.13 to 0.24 in 100,000. The vast majority of infections have occurred in unvaccinated individuals.

From 1990 through 1999, 117 cases of confirmed or probable CRS have been reported in the U.S. Almost one-third of patients with CRS can be linked to one of two rubella outbreaks in the United States. One outbreak occurred in California in 1989, while the other occurred in a Pennsylvania Amish community in 1991. On average, only six cases of congenital rubella have been reported each year from 1992 through 1999. Since 1993, CRS is seen far more commonly in neonates delivered to immigrants from regions without compulsory rubella immunization.

The transplacental transmission of rubella occurs during the viremic phase of primary maternal infection, generally a week before the appearance of a rash. Up to 20% of maternal infections occurring in the first 8 weeks of gestation result in miscarriage. Fetal infections occur in 90% of pregnancies when the maternal infection occurred during the first trimester, 25% to 30% during the second trimester, and 53% during the third trimester. The incidence of fetal anomalies varies according to the gestational age at the time of the maternal infection. If rubella infection occurs during gestational weeks 1 to 4, the incidence is 61% compared to 26% for weeks 5 to 8, 8% for weeks 13 to 16, and approximately 1% for subsequent weeks. Most studies report no excess defects in children whose mothers became infected at 18 weeks gestation or later.

Fetal damage is most likely multifactorial and may be secondary to rubella-induced apoptosis, decreased cellular life span, and necrotizing vasculitis. Clinical affects can be seen at the time of delivery or not until years after birth. In contrast to acquired rubella infection, congenital infection results in a persistent, progressive infection. Congenitally infected infants continue to excrete the virus in large quantities for months or even years, despite the presence of circulating antibody.

Neonates with CRS who were infected early in gestation generally have multisystem involvement and a spectrum of anomalies (Box 82.1 and Table 77.1) Symptomatic infants infected later in gestation may only have focal involvement of the eye or auditory system. Transient findings in the newborn period include generalized lymphadenopathy, hemolytic anemia, pneumonitis, hepatosplenomegaly, thrombocytopenia, and jaundice. “Blueberry muffin” lesions on the skin reflect focal areas of dermal erythropoiesis (see Color Figure 82.1 and in the color section). Most transient manifestations resolve within weeks of delivery.